Accuray Trust me when I say that my wife acts very much in the same way. Your example of throwing a rope to save her, and then her getting mad because you did really resonated to me.
Whether she accepts help or not does not change the fact that she is probably suffering from depression. That's like saying someone doesn't have cancer because they refuse chemo.
Staying with that metaphor it's like she chooses to self medicate with pain killers her cancer in order to avoid a scary surgery or difficult chemo. The fact that she chooses to pick fights with you is not necessarily your fault, but her using anger to relieve the depression she is feeling. For some (to include my W) picking a fight is easier than accepting sadness. You in essence get scapegoated. When my W is irritable out of nowhere it clues me in to know that she must not be feeling too well.
In my opinion your best course of action is to not get involved in her anger, let her calm down and then tell her that anger does not solve anything, but just makes things worse.
She may start saying that she is not good for you, because she knows no other way. In that case calmly and lovingly tell her that you want to build a good marriage, and that anger is not part of one. It's going to be hard, but it's something you can both work on together.
Trust me the first couple of times you'll probably get more anger. Just stay calm, and remind her that you are both working together towards a good marriage.
She also needs to learn better ways of self soothing. When she is feeling down make sure she gets lots of space to work through her own concerns.
Right now it is easier to pick fights when she feels too down. It is her coping mechanism. Take away yourself from that equation. It'll be rocky since she will be angry at you for taking away her coping mechanism of being angry at you. (crazy huh). IMHO it's for the best though, eventually she'll have to learn to cope without it or she'll have to find a healthier way of dealing with it.
